1. Technical Field
The present invention relates to a power conversion apparatus that includes a switch circuit, a feedback means and a signal generating means.
2. Related Art
In a burst mode operation based on conventional art, some switching frequency that falls in an audible frequency band may cause audible noise. Therefore, a technique has been developed, aiming to avoid such frequency that causes audible noise. An example of such an invention is disclosed in a patent document JP-A-2008-092793, the invention being entitled “Method and apparatus for reducing audible frequency in a switching power supply”. According to the technique, control is exerted over periods corresponding to groups of switching cycles of a switch, and over non-switching periods corresponding to intervals between the groups of switching cycles of the switch.
According to the technique disclosed in JP-A-2008-092793, when a turn-on period of a switch exceeds a threshold that indicates a small load, fixed frequency pulse-width modulation is merely changed to multicycle modulation, on the basis of the turn-on period of the switch. In an application of an in-vehicle DC/DC converter, for example, in which input/output voltage of a vast range varies, an amount of load can change a primary-side current peak, depending on the input/output voltage. Therefore, in the case where a fixed threshold is applied to the turn-on period, load current may vary to a large extent when the operation mode is switched to a burst mode. This may raise a problem of impairing the system efficiency over the entire operating range.